One major goal of the third-generation mobile communication system is to provide QoS (Quality of Service)-guaranteed multimedia services. In order to satisfy the requirement of the increased speed for the high-speed mobile data service especially for the mobile Internet service, an enhanced technique of UMTS, namely High Speed Downlink Packet Assess (HSDPA), is proposed in the recent 3GPP Release 5.
The primary purpose of implementing the HSDPA access scheme is to enable the WCDMA to support the transmission that may reach a peak rate of 8-10 Mbps in carrying out the downlink data packet services while achieving much lower transmission delay with a higher system capacity. Hence, the HSDPA process employs further enhanced technologies such as Adaptive Modulation and Coding (AMC), hybrid automatic repeat request (H-ARQ), fast cell selection (FCS) and multiple-input-multiple-output (MIMO) antenna processing. In the meantime, the HSDPA process is implemented with a new transmission channel, i.e., the High Speed Downlink Shared Channel (HS-DSCH). The HS-DSCH channel is designed with a smaller transmission timing-interval (TTI) that can be as small as 2 ms, thus enable the HSDPA process to achieve a faster dispatch of data packet, a smaller delay of HARQ and a faster channel adaptation of AMC. Furthermore, in order to reduce complication caused by UE and downlink signaling, the HS-DSCH channel adopts the Orthogonal Variable Spreading Factor (OVSF) codes. These codes have fixed spreading factor of 16. By using the time division multiplex (TDM) and code division multiplex (CDM) to share the system resource further improves the utilization ratio.
In general, a mobile communication system implemented with WCDMA uses the OVSF channel codes to achieve the dynamic allocation of the resource of system bandwidth and to provide variable data rates, thereby supporting various service bandwidth demands. FIG. 1 shows the tree structure for generation of the OVSF channel codes. Due to the limited numbers of codes available, the OVSF channel codes are considered as a scarce system resource in a system implemented with the WCDMA technologies. Furthermore, since the system utilization ratio is impacted by the orthogonal properties of the OVSF codes and the code assignment rule, how to reasonably use the OVSF code resource becomes an important design consideration for the Radio Resource Management (RRM) functions in a Radio Network Controller (RNC).
In a system implemented with the HSDPA access process, the OVSF channel codes employed for application to the HS-DSCH channel by definition have a fixed length of 16, e.g., C16,1 . . . C16,16 as that shown in FIG. 1. For a HS-DSHS channel the range of code selection is clearly defined. On the other hand, the protocol stipulates that a maximum of 15 OVSF channel codes with a length 16 can be used simultaneously for multi-code transmission of CDM in order to improve the instantaneous peak rate of the downlink shared channel. Since the OVSF codes are shared by various channels, the OVSF code resource with SF=4, 8, 16, . . . 512 is quite finite in the current WCDMA system. The R5 standard specification of 3GPP specifies maximum 15 SF 16 OVSF codes in HSDPA. Therefore, how to effectively use the finite OVSF code resource in the WCDMA system employing the HSDPA technology becomes a technical challenge. Since HSDPA service is carried on HS-DSCH channels and that specifies a maximum of 15 SF 16 OVSF codes, it is possible that the HSDPA service may not use so many OVSF code resources in a long period. In the meanwhile common DCH service lacks available OVSF resources in view of the HSDPA service burst and OFSF codes generation mechanism. By adopting a fixed allocation scheme for reserving HS-DSCH code, i.e., a certain number (less than or equal to 15) of OVSF codes are reserved for use in the HSDPA service, reduces the available DCH codes thus resulting in wastes of code resource without any beneficial effect of improving the system capacity.
Therefore, how to effectively manage and use these 15 HS-DSCH channel codes with a fixed length of 16 is an important design consideration for carrying out the HSDPA access in order to improve the system resource utilization ratio and system capacity. Due to the particular characteristics of the HS-DSCH channel codes, namely the fixed length of 16 and the maximum assignable 15 channel codes, the management of HS-DSCH channel code is entirely different from common management of other channel codes and must be handled with special cares.
Many existing researches on the management and assignment of the OVSF channel code resource merely take the assignment of common dedicated channel (DCH) codes into consideration. Such prior art disclosures include Chinese Patent Application No. 01105656.8 entitled “ALLOCATION METHOD OF SPREADING CODES IN WIDEBAND CMDA SYSTEM”, a Chinese Patent Application No. 01112812.7 entitled “CODE ALLOCATION METHOD IN CDMA SYSTEM”, Chinese Patent Application No. 01131225.4 entitled “ALLOCATION METHOD OF OVSF CODES”, Chinese Patent Application No. 01131226.2 entitled “OPERATION AND MAINTENANCE METHOD OF OVSF CODES” and Chinese Patent Application No. 01138087.X entitled “DYNAMIC AND OPTIMAL ALLOCATION METHOD OF CHANNELIZATION CODE RESOURCE IN WIDEBAND CDMA SYSTEM”.
All the code allocation methods disclosed in these patent applications consider only the process of the code allocation of the overall OVSF code tree by simply providing specific algorithms to manage the task of the code allocation. These prior art disclosures fail to take into account of the operation characteristics and mode of service supported by the HSDPA process and the code requirements of the HS-DSCH channels. In addition, in assigning the DCH codes, none of the existing code allocation algorithms considers the utilization ratio of the assigned code resource. Specifically, the assigned code resource is occupied till the service applying for a DCH is ended. At the end of the DCH service the assigned code resource is automatically withdrawn. However, after a cell is established, the HS-DSCH channel, different from DCH, is kept active continuously and shared by all users while assigning only those OVSF codes with a fixed length of 16 and using simultaneously of a maximum 15 codes. However, the operational schemes and methods of code allocation are restricted by the code tree assignment, while the strategy of adoption of the fixed reserving codes to reach the peak rate inevitably leads to waste of resource utilization.
In addition, some existing code allocation algorithms consider processing a service request class with respect to a data having a constant rate in most cases. However, services employing the HSDPA transmission, e.g., Internet browse, Internet games, download of e-mail annexes and download of audio and video media streams, have requirements of relatively small delay and bandwidth to handle burst transmission particularly for service of data transmission. The code allocation algorithms disclosed by the prior art do not provide appropriate measurement index for rates or bandwidth requirements in order to satisfy these operational requirements. An urgent need still exists to provide solutions in order to satisfy these requirements, particularly for services that demand a higher bandwidth rate.